Soon, devices that convert heat into electricity

Scientists are working on a novel technology that will allow future electronic devices to convert heat into electricity.

Previously researchers from Ohio State University in the US pioneered the use of a quantum mechanical effect to convert heat into electricity. Now, they have figured out how to make their technique work in a form more suitable to industry.

They used magnetism on a composite of nickel and platinum to amplify the voltage output 10 times or more - not in a thin film, as they had done previously, but in a thicker piece of material that more closely resembles components for future electronic devices.

Many electrical and mechanical devices, such as car engines, produce heat as a byproduct of their normal operation.

It is called "waste heat," and its existence is required by the fundamental laws of thermodynamics, researchers said.

However, a growing area of research called solid-state thermoelectrics aims to capture that waste heat inside specially designed materials to generate power and increase overall energy efficiency.

"Over half of the energy we use is wasted and enters the atmosphere as heat," said Stephen Boona, a postdoctoral researcher at Ohio State.

"Solid-state thermoelectrics can help us recover some of that energy. These devices have no moving parts, don't wear out, are robust and require no maintenance. Unfortunately, to date, they are also too expensive and not quite efficient enough to warrant widespread use. We're working to change that," said Boona.

In 2012, the research group, led by Joseph Heremans, demonstrated that magnetic fields could boost a quantum mechanical effect called the spin Seebeck effect, and in turn boost the voltage output of thin films made from exotic nano-structured materials from a few microvolts to a few millivolts.

In the latest advance, they have increased the output for a composite of two very common metals, nickel with a sprinkling of platinum, from a few nanovolts to tens or hundreds of nanovolts - a smaller voltage, but in a much simpler device that requires no nanofabrication and can be readily scaled up for industry.

Heremans said that, to some extent, using the same technique in thicker pieces of material required that the team rethink the equations that govern thermodynamics and thermoelectricity, which were developed before scientists knew about quantum mechanics.

While quantum mechanics often concerns photons - waves and particles of light - Heremans' research concerns magnons - waves and particles of magnetism.

"Basically, classical thermodynamics covers steam engines that use steam as a working fluid, or jet engines or car engines that use air as a working fluid.

"Thermoelectrics use electrons as the working fluid. And in this work, we're using quanta of magnetisation, or 'magnons,' as a working fluid," Heremans said.